The mutagenic and carcinogenic activities of previously untested electrophilic agents were investigated. Polymerase A-deficient and WP2(hcr-) E. coli and Salmonella TA 1535 and TA 100 were used in standard plate tests to determine the mutagenic and growth inhibitory activities of the alkyl halides. The ability of alkyl halides to produce lung adenomas in strain A mice was also studied. In general, branching and ease of dissociation increased both the mutagenic and carcinogenic activities of the alkyl halides. However, the addition of polar substituents to alkyl bromides made them too toxic to test for carcinogenic activity, while they retained their mutagenic activities. BIBLIOGRAPHIC REFERENCES: Poirier, L.A.: Mutagenicity prescreens for chemical carcinogens. In Montesano, R., Bartsch, H., and Tomatis, L. (Eds.): Screening tests in Chemical Carcinogenesis. IARC Scientific Publication #12, pp. 15-24, Lyon, 1976. Poirier, L.A. and Simmon, V.F.: Mutagenic-carcinogenic relationships and the role of mutagenic screening tests for carcinogenicity. Clin. Toxicol. 9: 761-771, 1976.